'\"
'\" Copyright (c) 2018 by Peter Spjuth.  All rights reserved.
'\"
'\" See the file "license.terms" for information on usage and redistribution
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.TH lpop n 8.7 Tcl "Tcl Built-In Commands"
.so man.macros
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
lpop \- Get and remove an element in a list
.SH SYNOPSIS
\fBlpop \fIvarName ?index ...?\fR
.BE
.SH DESCRIPTION
.PP
The \fBlpop\fR command accepts a parameter, \fIvarName\fR, which
it interprets as the name of a variable containing a Tcl list.
It also accepts one or more \fIindices\fR into
the list. If no indices are presented, it defaults to "end".
.PP
When presented with a single index, the \fBlpop\fR command
addresses the \fIindex\fR'th element in it, removes if from the list
and returns the element.
.PP
If \fIindex\fR is negative or greater or equal than the number
of elements in \fI$varName\fR, then an error occurs.
.PP
The interpretation of each simple \fIindex\fR value is the same as
for the command \fBstring index\fR, supporting simple index
arithmetic and indices relative to the end of the list.
.PP
If additional \fIindex\fR arguments are supplied, then each argument is
used in turn to address an element within a sublist designated
by the previous indexing operation,
allowing the script to remove elements in sublists.
The command,
.PP
.CS
\fBlpop\fR a 1 2
.CE
.PP
gets and removes element 2 of sublist 1.
.PP
.SH EXAMPLES
.PP
In each of these examples, the initial value of \fIx\fR is:
.PP
.CS
set x [list [list a b c] [list d e f] [list g h i]]
      \fI\(-> {a b c} {d e f} {g h i}\fR
.CE
.PP
The indicated value becomes the new value of \fIx\fR
(except in the last case, which is an error which leaves the value of
\fIx\fR unchanged.)
.PP
.CS
\fBlpop\fR x 0
      \fI\(-> {d e f} {g h i}\fR
\fBlpop\fR x 2
      \fI\(-> {a b c} {d e f}\fR
\fBlpop\fR x end
      \fI\(-> {a b c} {d e f}\fR
\fBlpop\fR x end-1
      \fI\(-> {a b c} {g h i}\fR
\fBlpop\fR x 2 1
      \fI\(-> {a b c} {d e f} {g i}\fR
\fBlpop\fR x 2 3 j
      \fI\(-> list index out of range\fR
.CE
.PP
In the following examples, the initial value of \fIx\fR is:
.PP
.CS
set x [list [list [list a b] [list c d]] \e
            [list [list e f] [list g h]]]
      \fI\(-> {{a b} {c d}} {{e f} {g h}}\fR
.CE
.PP
The indicated value becomes the new value of \fIx\fR.
.PP
.CS
\fBlpop\fR x 1 1 0
      \fI\(-> {{a b} {c d}} {{e f} h}\fR
.CE
.SH "SEE ALSO"
list(n), lappend(n), lassign(n), lindex(n), linsert(n), llength(n),
lmap(n), lrange(n), lremove(n), lrepeat(n), lreplace(n),
lreverse(n), lsearch(n), lset(n), lsort(n),
string(n)
.SH KEYWORDS
element, index, list, remove, pop, stack, queue
'\"Local Variables:
'\"mode: nroff
'\"End:
